The present invention relates to a float positioning assembly for pilot operated valves, and more particularly, to an assembly which permits a greater percentage of available pilot pressure to be used during "raise" and "lower" modes of operation, thereby saving energy.
It is known to provide servo actuated proportional flow control valves for operating double-acting cylinders, fluid motors and similar devices. A flow control valve of this type includes a pilot servo actuator which effects axial movement of a valve spool to control fluid flow to the double-acting cylinder. The valve spool is movable by the servo actuator from a "neutral" position to either a "raise" or "lower" position depending upon the directional movement desired for the double-acting cylinder.
In many applications, it is necessary for the valve spool of the flow control valve to have an additional "float" position where the two working ports of the control valve are both simultaneously connected to a tank or reservoir. This is necessary so that an attachment that is connected to the double-acting cylinder may freely position itself in accordance with the forces acting upon it. The "float" position is typically located at one extreme end of the valve spool stroke, and the spool travel from the "neutral" position to the "float" position is approximately twice the spool travel from the "neutral" position to the "lower" position. In known proportional control valves, the valve spool is movable against a fixed position centering spring which returns the valve spool to a "neutral" position when the pilot servo actuator is not being operated.
For a pilot operated valve of the proportional electro-hydraulic type, the pilot pressure required to move the valve spool between the "neutral" and "float" positions is approximately twice the pilot pressure required to move the valve spool between the "neutral" and "lower" positions using a conventional centering spring arrangement. Thus, there has been a need for a device which will permit a much greater percentage of available pilot pressure to be used for proportional control in the normal "raise" and "lower" modes of operation and still return the valve spool to its "neutral" position if an electrical or hydraulic failure occurs.